Radio-frequency transmission and reception appliances usually require a carrier frequency or heterodyne frequency. This is used to effect frequency conversion between a baseband or intermediate frequency and a radio frequency. This normally involves an incoming signal being logically combined with the local oscillator signal in a radio-frequency mixer.
Particularly in the case of homodyne architectures and with the increasing signal bandwidth which is to be processed, it has become usual to perform quadrature signal processing. This in turn requires the local oscillator signal to be supplied to the radio-frequency mixer having been broken down into two orthogonal signal components. These two signal components have the same carrier frequency but differ by a phase offset of 90 degrees. Such a signal is understood as a complex oscillator signal in the present case.
A complex oscillator signal can be generated using an integrated oscillator, for example. The signal obtained in this manner at a carrier frequency is usually broken down into two signal components whose phases have been shifted through 90 degrees relative to one another, namely an inphase component and a quadrature component, between the oscillator and the frequency mixer. Complex signals of this type are therefore also called IQ signals.
FIG. 4 shows a known option for obtaining an IQ signal of this type. An oscillator 1 is provided which generates a carrier signal in the form of a differential signal VCON, VCOP. This signal is supplied to a divider 2 which outputs two signals with a 90-degree phase shift. The output signals from the divider are respectively again in the form of differential signals. Accordingly, the two connections for the inphase signal component are denoted by IN, IP, whereas the quadrature components are denoted by QN, QP. Each of these two function blocks 1, 2 has an associated BIAS current source 39, 40 which is used to provide respective quiescent currents. The oscillator 1 and the divider 2 are connected to one another either via buffers or by means of AC coupling. The output signals IN, IP; QN, QP from the arrangement in FIG. 4 have a particular phase noise component. Conflicting with this is the fact that the desire for ever higher signal quality and bandwidth in telecommunications means that the phase noise in the local oscillator signal needs to be reduced further and further.
The document US 2004/0008092 A1 specifies a system for generating quadrature signals with an oscillator and frequency dividers in a current path.